On Windows, the type of the size parameter of read() is an unsigned int, not long nor size_t:
http://msdn.microsoft.com/en-us/library/1570wh78.aspx

FileIO.read() of Python 3 uses a size_t type but also:

#ifdef MS_WINDOWS
    if (size > INT_MAX)
        size = INT_MAX;
#endif
...
#ifdef MS_WINDOWS
        n = read(self->fd, ptr, (int)size);
#else
        n = read(self->fd, ptr, size);
#endif


Using a size_t to parse the Python parameter would avoid an OverflowError and the function would be more portable. But it would not permit to read more than 2 GB at once.